Adaptive Responses

Goals

• Motivate the user by showing them how their body is responding to exercise.
• Show the user what their body's adaptive responses are right now and how they change over time.
• Display the adaptive responses they can expect to get from a specific workout definition and a specific exercise definition.

Background and strategic fit

The aim of the Afterburner adaptive response system is to model the various physiological responses of the user's body after exercise, allowing them to 'see' what is happening to their body and making the training process more real and tangible.

It is a core feature of Afterburner - to show the user how their body responds to various types of workout. In reality, our bodies respond in many different ways, making us fitter and more healthy. In Afterburner however, we group these adaptive responses (ARs) into four AR Types:

• EPOC (Excess Post-exercise Oxygen Consumption): after intense exercise, your body must replenish the energy stores (phosphocreatine, ATP and glycogen) that were used up during the workout. It must also continue to actively dissipate excess heat to return you to a stable temperature. These processes cause you to burn calories for a period after exercise. This increased calorie-burn causes you to consume more oxygen and this is how the effect is measured in a lab. The effect is very strong immediately after exercise but tails off quickly to a low level that can last for a couple of days.
• Muscular Strength Adaptions: putting your muscles under 'exercise stress' creates micro-tears and causes them to adapt by strengthening themselves. This process is called muscular hypertrophy and can occur for up to 72 hours after exercise. Exercises that put a high resistance on a muscle cause a greater physiological response.
• Cardiovascular Adaptions: in the same way, putting your heart and cardiovascular system under exercise stress cause them to adapt and strengthen. Your heart muscles get stronger and bigger (cardio hypertrophy) and are able to pump more blood per second; veins and arteries get bigger and are able to handle more blood per second; lung capacity increases as the lungs grow more alveoli and are able to pass more oxygen into the blood.
• Metabolic Adaptions: as fitness increases, your body is able to burn fat more effectively. This means fat can be used as the primary fuel at higher exercise intensities, making it easier for you to burn even more fat. The body also becomes better at regulating hormones such as insulin and ghrelin. These are the hormones that govern the body's hunger and fat storage mechanisms.

When a user completes a workout activity, we calculate what these four responses will look like over time. Each AR type has a 'default shape' when graphed over time. But, depending on the type of exercise performed, the duration of exercise, the level of intensity with which it was performed, and the user's fitness level, the size and duration of each response type will be very different. For example, performing push-ups, planks and lunges will elicit a different set of physiological responses from jumping jacks, running on the spot and step-ups - even if the intensity and duration are the same.

Specifications

We graph an estimation of the user's adaptive responses after a workout activity to allow us to display this data on the main Afterburner screen. Each of the four ARs reacts differently to variations in the mode, duration and intensity of exercise.

Modelling the adaptive responses

We model each AR type by creating base curves that define the typical shape of each response over the time following a workout activity. We then modify the magnitude and halflife of each curve according to the duration and intensity of the work done, and the current fitness level of the user.

This process is completed separately for each of the four AR types and each exercise definition states the effect it has on each type. The responses from separate workout activities are then combined to allow us to output a figure stating the level of a response at any point in time.

Calculation for a single adaptive response from a single workout activity

The diagram below shows the process for calculating a single response (cardiovascular) from a single WA at a specific elapsed time. Note that this is for a single AR type only (cardiovascular). The calculation is repeated for each of the four types. It is the same calculation but uses different inputs for each AR type.

After calculating the amount of response stress produced by the WA, this is used along with workout intensity and the user's fitness level to calculate a magnitude product and a halflife Product. These products are used to modulate the base curve of the response: The magnitude is used to scale the 'size' of the response - how big the response is. The halflife is used to scale the duration of the response.

The following diagram outlines the complete calculation:

A JavaScript Proof of Concept demonstrates the calculations in detail here: http://dev.impossible.am/afterburner/Response%20POC/

Typical response patterns:

The typical pattern of the four AR types after a single workout activity might look like this, when graphed over time:

How the adaptive response calculations are used

Adaptive response radar chart

The user's current adaptive responses are shown on the main screen of Afterburner and this immediate, ever-changing visual feedback is a central feature of the app.

The chart shows the four responses (combined from all recent workout activities) on a four axis radar diagram, with the pending impact credit figure show in the centre. As time passes, the size of the responses reduce. The user then completes a new workout to boost them back up again.

Workout Impact and credit calculations

The calculations for max / actual workout impact, and pending / realised impact credit all use at least parts of the adaptive response calculations as input.

Requirements

Questions

Below is a list of questions to be addressed as a result of this requirements document:

Not Doing